Consistency bounds on the Wilson coefficients received a lot of
attention recently in the context of \(2 \rightarrow 2\)  scattering, which is
also the subject of our paper. The basic tool to derive such bounds is
given by dispersion relations which express low-energy Wilson
coefficients as weighted sums of the discontinuity of the
amplitude. Unitarity constrains the form of the discontinuity of the
amplitude which can be further used to derive the bounds. The simplest
examples of this type constrain the sign of Wilson coefficients. More
interesting bounds arise when one accommodates constraints coming from
crossing symmetry. Including those leads to the two-sided bounds on
the Wilson coefficients [1]}, [2]}, [3]}, [4]}. In this way the ultraviolet
(UV) complete theories form bounded regions in the space of
couplings.
Ref. [3]} also analyzed a few examples of physical EFTs
in the context of scattering of scalars and noted that they lie near the boundaries of the allowed region due to
the importance of low-spin contributions to the partial-wave
expansions (see Sect. 10.3 and Appendix D of Ref. [3]}).
